1. Field of the Invention
This invention relates to a combination steam reforming-hydroconversion process for light hydrocarbon feeds wherein the hydrocarbon and steam are passed over a sulfur-resistant catalyst which performs the dual function of steam reforming and hydroconversion of the feed. More particularly, this invention relates to a process for steam reforming and hydroconverting a relatively light hydrocarbon that is relatively low in hydrogen and high in sulfur, which comprises passing steam and the hydrocarbon over a sulfur-resistant catalyst comprising molybdenum on a base selected from the group consisting of (a) a high surface area alumina base or (b) an iron oxide-chromium oxide base, said catalyst having been reduced and sulfided prior to use, whereby the steam reforming and hydroconversion are achieved in the same reaction zone.
2. Description of the Prior Art
Steam reforming is well known to those familiar in the art as a process for producing hydrogen or hydrogen-containing gas mixtures by converting hydrocarbons with steam. The hydrocarbon reacts with steam to form carbon monoxide and hydrogen in a gasification reaction. The carbon monoxide is then reduced to a low level by a water gas shift reaction, which also produces more hydrogen. The two reactions combine in steam reforming as illustrated by the following equations. EQU Steam reforming: C.sub.n H.sub.2n +2nH.sub.2 O.fwdarw.3nH.sub.2 +nCO.sub.2 EQU =(a) gasification: C.sub.n H.sub.2n +nH.sub.2 O.fwdarw.2nH.sub.2 +nCO EQU +(b) water gas shift: nCO+nH.sub.2 O.fwdarw.nH.sub.2 +nCO.sub.2
one of the more commonly used catalysts for steam reforming is nickel oxide. Nickel oxide catalysts are very reactive and steam resistant. Unfortunately, however, these catalysts are not resistant to sulfur and, consequently, their catalytic activity rapidly diminishes to an unacceptably low level in the presence of sulfur-containing hydrocarbons. Platinum and other noble metal containing catalysts are also quite active for steam reforming hydrocarbon fractions, but these too are rapidly poisoned by relatively small quantities of sulfur in the feed. Catalysts commonly used for the water gas shift reaction include iron/chromium oxide and zinc/copper oxide catalysts, while the more efficient hydrogenation catalysts contain one or more noble metals. These catalysts are also poisoned and deactivated by sulfur. Unfortunately, many of the well known sulfur tolerant hydrogenation catalysts are deactivated in the presence of steam and are therefore totally unsuitable in the steam reforming process.
The petroleum industry is increasingly turning to coal, tar sands and heavy crudes as sources for future raw materials. Feed stocks derived from these heavier materials are quite naturally heavier but they are also more hydrogen deficient and higher in sulfur and nitrogen than feed stocks derived from more conventional crude oils. These heavier feed stocks therefore require a considerable amount of upgrading to usable products, such upgrading being accomplished by various hydroconversion reactions such as hydrodesulfurizing and hydrogenating, both of which require large volumes of hydrogen and consequently result in very high processing costs. One way of processing such feeds is to pass the sulfur-containing feed to a first zone wherein sulfur is removed via contact with a hydrodesulfurization catalyst, followed by a steam reforming zone wherein the desulfurized feed is contacted with steam and a catalyst to convert a minor portion of the feed to hydrogen, followed by passing the feed and hydrogen from the steam reforming zone to a third zone wherein the unsaturated portions of the feed are saturated by catalytic hydrogenation. Further, steam reforming is endothermic in nature requiring heat input to the reaction zone, while hydrogenation is exothermic.
It is apparent therefore, that it would be a significant improvement to the art if one could develop a process and steam and sulfur-resistant dual-function catalysts which would permit combining the endothermic hydrocarbon-steam reforming reaction to produce hydrogen and, at the same time, allow in situ utilization of the hydrogen produced by the steam reforming to saturate the olefins present in the feed and hydrodesulfurize same, all in the same reaction zone. This would eliminate the need for a separate source of hydrogen, eliminate the need for the plurality of reaction zones heretofore required for such processing and also result in substantial energy savings, because the exothermic hydroconversion reactions would provide at least a portion of the heat required for the endothermic steam reforming.